1. Field of the Invention
Embodiments of the invention relate to a method of manufacturing a silicon carbide semiconductor device.
2. Description of the Related Art
Research has been underway concerning semiconductor devices that use silicon carbide (SiC) as a semiconductor material (hereinafter, silicon carbide semiconductor devices) to realize high-voltage, low-loss semiconductor devices such as transistors, diodes, and the like. In the manufacturing process of a silicon carbide semiconductor device, an impurity that forms carriers (electrons, holes, etc.) is implanted in a semiconductor substrate formed from silicon carbide (hereinafter, silicon carbide substrate) and thereafter, the impurity is activated by heat treatment at a temperature of 1500 degrees C. or higher (hereinafter, activation annealing) to efficiently generate carriers.
However, when such high-temperature heat treatment is performed in a state in which the surface of the silicon carbide substrate is exposed, a problem arises in that surface roughness occurs consequent to sublimation (vaporization) at the surface of the silicon carbide substrate and characteristics of the silicon carbide semiconductor device significantly degrade. Therefore, to reduce the surface roughness of the silicon carbide substrate, typically, the activation annealing is performed in a state in which the surface of the silicon carbide substrate is covered by a cap layer formed from carbon (C) (protective film, hereinafter, carbon cap) (for example, refer to Japanese Patent Laid-Open Publication No. 2012-227473).
As another method of reducing surface roughness of the silicon carbide substrate, a method has been proposed in which a main surface of the silicon carbide substrate is a surface that includes a (0-33-8) face on which surface roughness does not substantially occur with high-temperature heat treatment and thus, the high-temperature heat treatment is performed without the formation of a cap layer (for example, refer to Japanese Patent Laid-Open Publication No. 2012-038771). Another method has been proposed in which activation annealing is performed in a state in which the surface of the silicon carbide substrate is covered by an oxide film (SiO2 film) or a silicon carbide layer acting as a cap layer (for example, refer to Japanese Patent Laid-Open Publication Nos. 2009-146997, 2009-272328, and 2015-135892).